Carbon deposition apparatus



Oct. 9, 1962 T. E. NANCE CARBON DEPOSITION APPARATUS Filed April l, 1959 V INVENTOR Zklf/?w BY (e 4 W ATTORNEY 3,057,325 CARBON DEPOSITION APPARAT US Taylor E. Nance, Winston-Salam, N.C., assignor to Westem Electric Company, Incorporated, New York, N .Y., a corporation of New York Filed Apr. 1, 1959, Ser. No. 803,529 Claims. (Cl. 118--47) This invention relates to a deposition apparatus and more particularly to an apparatus for depositing a uniform coating of carbon on ceramic cores while rolling the cores through a deposition chamber.

It is the purpose of the invention to form such articles as deposited carbon resistors by depositing a coating of carbon on a refract-ory body such as a ceramic core by heating the core to a predetermined temperature and then exposing the preheated core while in a rolling condition to an atmo sphere of carbonaceous gas in a coating chamber so that the gas is cracked and the carbon contained in the gas is deposited on the surface of the ceramic core. The carbon coating produces highly desirable resistance characteristics. By accurately controllng the deposition process, and thus the amount of carbon deposited, a deposited carbon resistor within extremely close resistance tolerances may be formed. By maintaining a fiow of ceramic cores through the carbon deposition chamber, great quantities of precision resistors or other articles can be continuously produced.

The density and thickness of the carbon coating formed on the ceramic cores is dependent on the length of time the core is exposed to the coating gas, the concentration of hydrocarbon in the coating gas, and the temperature to which the core is heated. These factors are critical and care is necessary to secure a uniform coating of hard carbon on the ceramic core without forming soot or soft carbon deposits.

Numerous attempts have been made to devise a carbon deposition apparatus capable of coating a continuous stream of ceramic cores while at the same time consistent- -ly 'obtaining predetermined results at a satisfactory production rate. These attempts have failed because of the difliculty in conveying a continuous stream of ceramic cores through a carbon deposition chamber while at the same time precisely controlling the length of time that the ceramic cores are exposed to the coating gas. This is caused by reason of the fact that no efiective manner of scaling the entrance and exit passages through which the articles must pass into and 'out of the deposition chamber has been devised so as to prevent the articles from being exposed to the coating gas prior to their being received in the deposition chamber or during their departure therefrom.

Another inherent dilficulty in present day techniques of coating articles as they pass through a deposition chamber is that of rotatively supporting an article While at the same time exposing the entire surface area of the article to the coating gas.

An object of this invention is to provide an apparatus for depositing a uniform coating of carbon on articles.

Another object of this invention is to provide an apparatus for depositing a uniform coating of hard carbon on ceramic cores as they are continuously rolled through the coating apparatus.

To accomplish these and other objects carbon deposition apparatus embodying certain features of this invention may include a preheating chamber, a deposition chamber, and a cooling chamber. A conveyor rolls ceramic cores through the deposition chamber at a uniform rate of speed where a carbonaceous gas is cracked or pyrolized and a uniform coating of carbon is deposited on the ceramic cores. A gaseous atmosphere excludes `the carbonaceous gas from the preheating and cooling 3,057,325 Patented Oct. 9, 1962 ice chambers exposing the articles to the carbonaceous gas in the deposition chamber only.

More specifically carbon deposition apparatus for carbon coating articles such as ceramic cores includes a preheating chamber, a coating chamber, and a cooling chamber. Electrical heating elements maintain the deposition chamber at the correct temperature so as to pyrolize or crack a carbonaceous gas forced through the chamber causing the carbon in the gas to be deposited on articles which are rolled through the apparatus between spaced guide rolls.

The articles are conveyed through the preheating chamber in an entrance tube which surrounds the guide rolls and opens into the deposition chamber. An outer tube spaced from and concentric With the entrance tube forms a closed passage around the entrance tube. Radially spaced ports in the end of the entrance tube adjacent the deposition chamber open into the closed passage surrounding the entrance tube permittng a neutral or inert gas to flow from a suitable source through the entrance tube and into the surrounding passage. An exhaust pump maintains suflicient pressure in the passage to exhaust the neutral gas from the entrance tube whereby the coating gas is excluded from the entrance tube. The spaced guide rollers roll the coated articles from the deposition 'chamber through a cooling chamber within an exit tube.

An atmosphere of neutral gas excludes the coating gas from the exit tube while an exhaust pump removes the coating gas and the neutral gas from the deposition chamber.

A clear Understanding of the invention will be had from the following detailed description of a specific embodiment thereof, When read in conjunction with the appended drawings, in which:

FIG. 1 is a cross-sectional View of a carbon deposition apparatus;

FIG. 2 is a partial plan view of a carbon deposition apparatus; and

FIG. 3 is a cross-sectional view taken along line 3-3 of FIG. 1.

Referring to the drawings a furnace tube 11, composed of a refractory material and having headers 12 and 13 of fused silica, extends through an electric furnace 14. The furnace 14 is heated by electrical elements 15 spaced around and along the furnace tube 11. The elements 15 are connected in parallel and are energized from a suitable voltage source 16. A central portion 17 of elements 15 extend through a heating chamber 18, which is formed of fire brick or other heat insulating material. The heating chamber 18 surrounds the furnace tube 11 and defines a central hot zone within the furnace 14. A cylindrical furnace lner 19 of a highly heat conductive material such ras silicon carbide is secured within the furnace tube 11 and defines a deposition chamber 21.

An entrance tube 22 secured .to the inner face of the header 12 extends through and defines a preheating chamber 23 within a portion of the furnace tube 11. The entrance tube 22 and the preheating chamber defined thereby open into the deposition chamber 21. An outer tube 24 mounted concentric with the entrance tube 22 and spaced from the furnace tube 11 is rigidly secured to an inner side wall face of the header 12. An end cap 25 secured to the end of the outer tube 24 and the entrance tube 22 adjacent the deposition chamber 21 forms a closed passage 26 between the entrance tube 22 and the outer tube. Radially spaced ports 27 formed in the end of the entrance tube 22 open into the closed passage 26.

An exit tube 28 secured to the inner face of the header 13 extends through and defines a cooling chamber 29 within a portion of furnace tube 11. The exit tube 28 and the cooling chamber 29 defined thereby opens into the deposition chamber 21.

A suitable source of carbonaceous coating gas 31 such as methane and intermixed with a suitable carrier gas such as nitrogen is connected through a tube 32 into a passage 33 surrounding the outer tube 24 which opens into the deposition chamber 21. An exhaust pump 34 is connected with a passage 35 surrounding the exit tube 28 and which opens into the deposition chamber 21. The exhaust pump 34 draws the coating gas through the passage 33, the deposition chamber 21, and out through the passage 35 into the atmosphere or a suitable gas collector. The coating gas is diffused throughout the deposition chamber 21. The type of coating gas which may be used is not restricted to methane or other gases in the methane series. As is well known, many other types of gas rich in hydrocarbon may be employed. By the proper choice of coating gas, and additives mixed therewith if desired, and of the temperature within the deposition chamber, the carbon in the gas will be deposited as a hard film on articles exposed to the coating gas within the deposition chamber 21. By controlling the duration and manner of exposure of the article to the coating gas a uniform film of hard carbon will be deposited on the article. This film when deposited on ceramic cores or other refractory bodies gives the core a very desirable resistance characteristic. In the manufacture of deposited carbon resistors it is mandatory that the physical characteristics of the carbon coating formed on ceramic cores be precisely controlled in order to produce the desired resistance value within close tolerances.

A conveyor assembly 36 for transporting a series of ceramic cores 37 or other refract'ory bodies through the furnace 14 comprises a pair of spaced parallel guide rolls 38 and 39 rotatively supported at both ends and within base pans 41 and 42. The guide rolls 38 and 39* and their respective base pans 41 and 42 pass through apertures 40 in the headers 12 and 13, the entrance tube 22, the deposition chamber 21, and the exit tube 28, respectively.

As shown in FIG. 2, a spiral groove 43 of rectangular cross section is formed in each of the guide rolls 38 and 39 and extends along their length. The grooves 43 are identical in pitch, one groove forming a left-hand thread in guide roll 38 and the other forming a right-hand thread in the guide roll 39.

The ceramic cores 37 are supported between and perpendicular to the spaced guide rolls 38 and 39` on an upturned edge 44 formed on each of the base pans 41 and 42 while the ends of the ceramic cores 37 are received in the spiral grooves 43. 'Ihe core 37 is preferably supponted such that its horizontal axis will lie in a plane extending between the horizontal aXes of the guide rolls 38 and 39.

Intermeshing gears 45 are Secured t'o a reduced end portion 46 -on each of the guide rolls 38 and 39. A drive gear 47, fixed to a shaft 48 which is driven by a motor 49, meshes with one of the gears 45 to rotate the gears 45 and the guide rolls 38 and 39 in opposite directions. The guide rolls 38 and 39` may be driven by separate motors if desired. The shaft 48 passes through a seal in the wall of a feeding chamber `51 formed around the end of the guide rolls 38 and 39 and Secured to the header 12.

A hopper 52 mounted above the guide rolls 38 and 39 and extending through the feeding chamber 51 supports a vertical column of horizontally disposed ceramic cores 37 directly over the spaced guide rolls 38 and 39. The ceramic cores 37 are fed into the hopper 52 through a supply tube 53. The cores 37 are supported within the hopper 52 on slides 54 which are alternately reciprocated by pneumatic or other suitable means (not shown) to feed the ceramic cores 37 one at a time to the guide rolls 38 and 39. As the cores 37 fall from the hopper 52, they are supported on the edge 44 of the base pans 41 and 42, and the ends of the cores are received within the spiral grooves 43. Due to the counter-rotation of the guide rolls 38 and 39 and the opposite threads formed by the spiral grooves 43, the ceramic cores 37 Will be simultaneously rotated and conveyed through the furnace 14 where they are uniformly coated with carbon. The speed of rotation and horizontal movement of the ceramic cores may be varied by adjusting the speed of the motor 49 and varying the pitch of the spiral grooves 43. The ceramic cores 37 are supported by and rotate upon the edges 44 of the base pans 41 and 42.

The ceramic cores 37 pass through the furnace 14 between the guide rolls 38 and 39' into a receiving chamber 55 Secured to the header 13. An end portion 56 of each of the guide rolls 38' and 39 is reduced in diameter to the depth of the spiral grooves 43 and is supported in a suitably mounted bearing '57. A hopper 58, supported directly below the reduced end portions 56 and extending through the receiving chamber `55 receives the carboncoated cores 37 as they roll out of the spiral grooves 43 formed in the guide rolls 38 and 39. The cores 37' are supported within the hopper 58 on one or the other of a pair of alternately reciprocable slides 59 which are actuated by pneumatic or other means (not shown). As the slides 59` are reciprocated the cores 37 pass from the hopper 58 into a discharge tube 61 which transports the cores to a next desired position.

A neutral gas such a nitrogen, supplied under pressure from a pump 62. in a tube 63, passes into the feeding chamber 5 1 and through the aperture 40 into the entrance tube 22. The nitrogen gas provides a protective atmosphere within the feeding chamber '51, preventing the cores 37 from being contaminated before entering the furnace 14. An exhaust pump 64', connected to the passage 26 through a tube 65, draws the neutral gas through the feeding chamber 51, the entrance tube 22, the radial-ly spaced ports 27, and through the passage 26 into the atmosphere. By maintaning a negative pressure in the passage 26 by means of the pump 64 the neutral gas is withdrawn with sufiicient velocity so as to prevent the neutral gas from entering the deposition chamber 21 or the coating gas from contacting the ceramic cores 37 until they enter the deposition chamber 21. As the cerarnic cores 37 are transported through the entrance tube 22 they are preheated to the desired temperature by the elements 15 surrounding the furnace tube 11.

A neutral gas such as nitrogen supplied under pressure from a pump 66 in a tube 67 passes into the receiving chamber 55 and through the aperture 40 into the exit tube 28. The nitrogen gas flows through and is swept out of the end of the exit tube 23 adjacent the deposition chamber 21 where it turns sharply and is exhausted by the pump 34 along with the coating gas and other products of the cracking process. The nitrogen gas excludes the coating gas from the exit tube 28 and provides a protective atmosphere in which the coated ceramic cores 37 are cooled before they are removed from the furnace 14.

operation Ceramic cores 37 are fed in seriation from the supply hopper 52 within the protective atmosphere of the feeding chamber 51 to the guide rolls 38 and 39 where they are received in the spiral grooves 43. As the guide rolls 38 and 39 are counter-rotated, the cores 37 -will be rotated along the edges 44 of the base pans 41 and 42 into the furnace 14. As the cores pass through the inert gaseous atmosphere maintained within the entrance tube 22, they are preheated to the desired temperature by the heating elements 15. The preheated cores 37 continue to rotate along the edges 44 of the base pans 41 and 42 into the deposition chamber 21 where they are exposed to a carbonaceous coating gas of methane supplied from the tank 31. The inert gas supplied by the pump 62 is drawn through the feeding chamber 51, the entrance tube 22, and the radial ports 27 into the passage 26 by the pump 64 with suificient velocity and pressure to seal the preheating chamber 23 -from the deposition chamber 21 and exclude the coating gas from the entrance tube 22.

&0573325 This action shields the ceramic cores 37 from the coating gas until they enter the deposition chamber 21.

As the ceramic cores 37 pass into the deposition chamber 21 they are heated to a desired final temperature. When the coating gas Contacts the heated cores 37, it is cracked and the carbon in the gas is deposited on the ceramic cores 37 as a hard film. Because of the spiral grooves 43 and the edges 44 of the base pans 41 and 42, the ceramic cores 37 are supported between the guide rolls 38 and 39, and are continuously rotated within the deposition chamber 21. The surface area of each of the ce'amic cores is evenly exposed to the coating gas assuring uniform coating. The speed of rotation of the ceramic cores 37 may be precisely regulated by adjusting the speed of the motor 49 or changing the pitch of the spiral grooves 43. The rate of travel of the cores through the furnace is controlled by adjusting the speed of motor 49. The conveyor assembly 36 can be readily adjusted to transport dierent lengths of articles by varying the spacing of the guide rolls 38 and 39 and adjusting the drive mechanism therefor.

As the coated cores 37 leave the deposition chamber 21 they enter a protective atmosphere of nitrogen or other inert gas within the exit tube 28. The nitrogen gas is supplied under pressure from a suitable source by the pump 66 and flows in a direction opposite to that of the ceramic cores 37. As the nitrogen gas passes out of the exit tube 28 it is turned sharply, and is withdrawn along with the coating gas and other products of the cracking process through the passage 35 by the pump 34. This action excludes the coating gas and other products of the cracking process from the exit tube 28 and provides a protectve atmosphere for the coated cores 37. The coated cores 37 are cooled as they pass through the exit tube 28 before entering the receiving chamber 55. The uniformly coated cores 37 remain within the spiral grooves 43 until they reach the reduced end portion 56 of the guide rolls 38 and 39 where they roll out of the grooves 43 into the hopper 58 where they are fed into the discharge tube 61 by the alternately reciprocating slides 59.

It is to be understood that the above described apparatus is simply illustrative of the application of the broad principles of the invention. Numerous other arrangements may be devised by those skilled in the art which will embody the principles of the invention and fall within the scope thereof.

What is claimed is:

1. Deposition apparatus for coating ceramic cores which comprises a preheating chamber, a deposition chamber, a cooling chamber, conveyor means for supporting only the ends of the ceramic cores and for rolling the ceramic cores through said preheating, deposition, and cooling chambers, means for conducting a carbonaceous coating gas through said deposition chamber, means for heating the deposition chamber to crack the gas and deposit a coating on the ceramic cores, and means for excluding the coating gas from the preheating and cooling chambers.

2. A carbon deposition furnace for coating ceramc cores comprising a deposition chamber, means for maintaining a continuous flow of a carbonaceous coating gas throughout said chamber, conveyor means for rolling the ceramic cores through the deposition chamber, an entrance tube through which articles to be coated are conveyed into the deposition chamber, an exit tube in which the articles are conveyed from the deposition chamber, and means for maintaining an inert gaseous atmosphere in the entrance and exit tubes whereby the articles to be coated are exposed to the coating gas only in the deposition chamber.

3. A carbon deposition furnace for coating ceramic cores comprising a deposition chamber, means for passing a carbonaceous coating gas through said chamber, means for exhausting the coating gas from said chamber, spaced rotatable members for receiving the ends of the ceramic cores and for rolling the ceramic cores in a direction normal to their longitudinal axes through the deposition chamber, an entrance tube through which articles to be coated are conveyed into the deposition chamber, means for heating the deposition chamber to crack the coating gas in the deposition chamber, an exit tube in which the articles are conveyed from the deposition chamber, a tube mounted concentrically with and surrounding the entrance tube, a cap on the end of the concentric tubes adjacent the 'deposition chamber forming a closed passage between the entrance tube and the concentric tube mounted therewith, notches formed in the end of the entrance tube and opening into said passage, and means for maintaining an inert gaseous atmosphere in the entrance and exit tubes whereby the articles to be coated are exposed to the coating gas only in the deposition chamber as they are conveyed through the furnace.

4. Apparatus for conveying cylindrical articles comprising a pair of spaced parallel guide rolls having opposite threads formed along their length, means for supporting the articles between the guide rolls and within the opposite threads formed therein, and means for counter-rotating the guide rolls whereby the articles are rotated within the opposite threads and along the length of the guide rolls.

5. Apparatus for rolling cylindrical bodes comprsng a pair of spaced guide rolls having opposite threads formed along their lengths, means for placing the cylindrical bodes between the guide rolls, means for supporting the cylindrical bodes between the guide rolls and within the opposite threads formed therein, and means for rotating the guide rolls in opposite directions whereby the cylindrical bodes are rotated within the opposite threads and rolled along the length of the guide rolls.

6. A carbon deposition furnace for coating cerarnic cores which comprises a preheating chamber, a deposition chamber, and a cooling chamber, spaced rotatable members for conveying ceramc cores to be coated through the preheating, deposition, and cooling chambers, means for conducting a carbonaceous gas through said deposition chamber, means for heating the deposition chamber to crack the carbonaceous gas, an entrance tube through which the ceramic cores to be coated are conveyed through the preheating chamber and into the deposition chamber, an outer tube spaced from and concentric with the entrance tube and forming a closed passage about said entrance tube, radial ports formed in the end of the entrance tube adjacent the deposition chamber and opening into said closed passage, a source of neutral gas connected to the entrance tube, a pump for withdrawing the neutral gas from the entrance tube through the radial ports and out the closed passage whereby the coating gas is excluded from said entrance tube, an exit tube in which the cores are conveyed from the deposition chamber and through the cooling chamber, a source of neutral gas connected to the exit tube, and a pump for withdrawing the neutral gas from the exit tube in a direction which is opposite to the direction of travel of the ceramic cores and for withdrawing the neutral gas and the coating gas from the furnace whereby the coating gas is excluded from the exit tube.

7. In a conveying apparatus, a pair of spaced supports, a pair of threaded members mounted for rotation above the outer edges of the respective supports, means for feeding articles between said members so that the ends project into the threaded members, and means for rotating said members to advance the articles along the supports.

8. In an article advancing apparatus, an elongated support, a pair of members having threaded sections, means for mounting said members for rotation above opposite edges of one surface of said support, means for feeding articles onto said support so that the ends project into the threaded sections, and means for rotating said threaded members to advance and roll said articles along said support.

9. In a coating apparatus, an entry chamber, a coating chamber at the terminus of and opening into said entry chamber, an exit chamber at the terminus of and opening into said coating chamber, means for supplying neutral gas to said entry chamber, means for exhausting said neutral gas from said terminus of said entry chamber, means for supplying a coating gas to said coating chamber, means for supplying neutral gas to said exit chamber, means for simultaneously exhausting said coating gas and said neutral gas at the entrance of said exit chamber, and means for rolling cylinclrieal articles through said entry, coating, and exit chambers.

10. Apparatus for transporting cylindrical bodies which comprises a pair of spaced Parallel guide rolls having identical but opposite threads formed along their lengths, a pair of spaced parallel base pans, each having an upturned edge secured beneath the guide rolls and extending along its length for supporting the cylindrical bodies between the guide rolls and within the opposite threads formed therein, and means for counter-rotating the guide rolls Whereby the cylindrical bodies supported between the guide rolls -are rotated within the opposite threads in the guide rolls and rolled along the upturned edges of the base pans.

References cited in the file of this patent UNITED STATES PATENTS 

